The present invention is directed to sheet fabrication machines and more particularly to a press brake with an improved sheet positioning system.
A typical press brake has a lower tool, typically referred to as a V tool or a die, and an upper tool that acts as a punch that mates with the lower tool. To bend a workpiece placed between the upper and lower tools, the lower tool may remain stationary while the upper tool acts thereagainst. Conversely, the upper tool may stay stationary while the lower tool would move up to act against a worksheet. These up and down motions by the upper and lower tools of the press brake are accomplished by using a number of known drive mechanisms, including for example a hydraulic drive by using one or more hydraulic cylinders, or a mechanical drive that utilizes a combination clutch and brake fly wheel system.
To bend a worksheet correctly, the worksheet has to be positioned to the correct position for each of the bends. Conventionally, positioning is determined by programmable stops, otherwise known in the art as back gauge xe2x80x9cfingersxe2x80x9d. These xe2x80x9cfingersxe2x80x9d are force sensors that are mounted to back gauges to the back of the press brake which are positioned some distance from the center of the upper and lower tools or punches. The positioning of the back gauges is automatic and is controlled by a CNC controller sending commands to a servo system. Servo systems that are used in the sheet fabricating art for driving the back gauges include Cyberlec, Siemens, Hurco and Automec, among others. The typical back gauge system has two back gauge fingers that are movable along an axis that is perpendicular to the direction along which the punch and die move. This axis is conventionally referred to as the X axis. The programmable fingers also are movable along a vertical axis, commonly referred to as the R axis. The back gauge fingers can also move either in a pair-wise fashion or independently, in which case there are independent X and R axes for each of the back gauge fingers. Independent back gauge fingers are used for those complicated bending operations that involve positioning references for different bends and/or a part that may have to be taken from two different heights or depths with reference to the center of the upper and lower tools along the X axis.
The various bending operations for effecting different bends to a worksheet are conventionally programmed into the CNC controller. The back gauges are used to ensure that the positioning of the worksheet for each bend is correct. To achieve this, an edge of the worksheet is pressed against the back gauge fingers, as the upper punch and the lower die would come together to effect the bend. After each bend the back gauge fingers would move to a new position in anticipation of the worksheet pressing against the fingers. This cycle of moving of the back gauges, the positioning of the worksheet and the pressing of the worksheet against the back gauge fingers is repeated for each bend of the worksheet.
The pressing of the worksheet of the to be fabricated part against the back gauge fingers is acceptable so long as the machine is either being operated by a human operator or is operating at a slow speed. However, for a press brake where the part positioning is being done by a robot, and if it is the pressing action on the back gauge fingers that is used to activate a switch or a pair of switches to indicate the correct location of the worksheet for bending, such conventional pressing of the back gauge finger sensors would act to slow down the bending operation. Moreover, given that the back gauges are driven by multiple servomotors, and their associated motion systems that may include bore screws, belts or linear gear systems for each axis of movement, physical deterioration of the drive system for the back gauges occurs. As a consequence, the positioning of the parts to be bent may not be as accurate as it should be. Accordingly, the bends on those parts may end up being out of tolerance.
To ensure accurate positioning of a worksheet or part for every bend in a press brake, and furthermore without having to worry about the back gauge system becoming inaccurate and/or breaking down, the present invention provides a contactless gauge system that can accurately ascertain the correct positioning of the worksheet for each bend of the worksheet and for compensating any deviation in the positioning of the worksheet.
Specifically, in place of a mechanical back gauge system, the present invention comprises an optical system that utilizes a laser system, an imaging system, and/or a combination of both. In one of the embodiments, a laser system is placed at a certain distance relative to the upper and lower tools at the backside of the press brake. By means of the non-contact sensors that work in conjunction of the output laser beams, the actual position of the workpiece could be determined. Once determined, the actual measured position of the worksheet is compared with the preprogrammed position of the worksheet for the particular bend. And if the desired programmable position matches that of the actual measured position, then the bending of the worksheet could proceed. This process of actually moving the worksheet, the sensing of the actual position of the worksheet, and the comparing of the actual position with the sensed position is repeated for each bend of the worksheet. If there happens to be a deviation between the programmed position and the measured position of the worksheet, then a further movement of the worksheet is made to move the worksheet to the programmed position before the bending of the worksheet commences.
Another embodiment of the present inventive non-contact measurement of the position of the worksheet could be effected by a camera monitoring system in which a view of the backside of the upper and lower tools of the press brake is taken. This image includes the end edge of the workpiece. The image is divided into appropriate coordinates so that a precise location of the end edge of the worksheet is measured. The measured edge of the worksheet is then compared with a stored image of what that end edge should be at if the worksheet were correctly positioned. If a comparison of the programmed image and the scanned image of the position of the worksheet matches, then the bending of the worksheet could commence. If not, additional movement of the worksheet is effected; and another image is taken after the additional movement of the worksheet so that yet another comparison is made between the measured image and the preprogrammed image to determine if further compensation or movement of the worksheet is required.
Yet another embodiment of the present invention involves the use of a combination of laser and imaging systems. In this embodiment, a number of laser beams are directed to the backside of the press brake so as to intersect the back edge of the worksheet. A monitoring camera then senses the multiple points at the edge of the worksheet intersected by the plurality of the laser beams. From these multiple intersected points, the CNC controller can calculate, by for example a triangulation method, the actual position of the worksheet. And by comparing the measured position with the preprogrammed position, any deviation to the positioning of the worksheet that occurs could be readily compensated, before actual bending of the worksheet takes place.
The inventor of the present invention further envisions a simple system that could be retrofitted readily to an existing back gauge system that nonetheless provides for contactless determination of the actual positioning of the worksheet. This is done in yet another embodiment of the instant invention in which sensors that could determine from a given distance the arrival or existence of a part are incorporated to the exiting back gauges of a press brake. This is done by replacing the conventional finger sensors with non-contact sensors, which could be sensors that work by determining the electromagnetic flux near it or laser sensors that could determine the edge of the worksheet at a predetermined distance. Thus, by utilizing the existing servomotors to drive the back gauges in a shadow movement to the movement of the worksheet at a given distance, the back gauges of such retrofitted sensing system would never come into physical contact with the edge of the worksheet insofar as the back gauges would always be at a safe distance from the edge of the worksheet. Any over movement on the part of the worksheet would cause a corresponding backward movement by the back gauge. The fact that the sensors mounted to the back gauge fail to detect the edge of the worksheet or that the back gauges in fact move further then they should after the CNC controller has terminated its movement of the worksheet means that there is a deviation, and the requisite compensation movement of the worksheet is then taken.
It is therefore an objective of the present invention to provide a system that can monitor without contact the precise location of a worksheet relative to the upper and lower tools of a press brake.
It is another objective of the present invention to provide a contactless worksheet gauge system that obviates the need for any moving system that would cause inaccuracy due to the wear and tear of the mechanical components over time.
It is yet another objective of the present invention to provide a contactless worksheet gauge system that enhances the operation of determining the precise location of a worksheet since the movement of the worksheet no longer has to slow down to make contact with any back gauge fingers.
It is still another objective of the present invention to provide a contactless worksheet position gauging system that can be retrofitted to an existing back gauge system of a press brake.